Here are this week's top must-read stories from #MuckReads, ProPublica's ongoing collection of the best watchdog journalism. Anyone can contribute by tweeting a link to a story and just including the hashtag #MuckReads or by sending an email to MuckReads@ProPublica.org. The best submissions are selected by ProPublica's editors and reporters and then featured on our site and @ProPublica.

Though Mauritania abolished slavery in 1981 (the last country to do so), an estimated 10 to 20 percent of the population remains in "real slavery," say human-rights activists. It’s an open secret, with the government ejecting journalists and allegedly arresting and torturing anti-slavery activists.

Companies with government contracts have been banned from donating to federal campaigns since 1976. But this year, thanks to a legal gray area introduced by the 2010 Citizens United case, federal contractors have given nearly million to the pro-Romney super PAC Restore Our Future. And at this point, no one seems sure whether the contributions are legal.

A Chinese firm sold a surveillance system to Iran's government-controlled telecom company, giving it the ability to monitor text messages, phone conversations and web access. Buying through China is also a backdoor way Iran can avoid sanctions and get access to U.S. technology.

The Center for Public Integrity, Public Radio International and Global Integrity teamed up for this “unprecedented, data-driven analysis” of states’ corruption risk. They graded states in 14 categories, measuring the strength of laws to deter corruption — not simply the number of scandals.

After a "Marketplace" reporter unearthed details that took down “Mr. Daisey and the Apple Factory,” the incredibly popular podcast that detailed horrific conditions at an iPhone manufacturer in China, This American Life had him help explain how they’d been duped. Mike Daisey, the monologuist who authored the original show, also was interviewed.

Walmart’s sustainability program has been lauded for its industry-wide influence. But under the watch of idle auditors, and amid an economic slowdown, the company's greening efforts seem to be slowing to a halt.